220.87 for EV charger Install load calculation in existing dwelling

[J2H]

Just wondering if there is any reason 220.87 can't be used to ensure an existing service is sufficiently sized for the addition of an EVSE.

 

[JoeStillman]

I have done that.

 

[jaggedben]

No, there is no reason it can't be used.

 

[don_resqcapt19]

With the smart meters, some utilities will provide the 15 minute demands to make such calculations easy.
Our utility will only provide 15 minute usage in kWH and not a 15 minuted demand for residential services.

 

[wwhitney]

Our utility will only provide 15 minute usage in kWH and not a 15 minuted demand for residential services.

Sorry, what do you mean by "15 minute demand"? I thought that was average power used over a 15 minute interval, so in units of kW it would just be 4 times 15 minute usage in kWh.

Or are you making the distinction between kVA and kW? Is the average power factor on a residential service significantly different from 1?

Cheers, Wayne

 

[jaggedben]

With the smart meters, some utilities will provide the 15 minute demands to make such calculations easy.
Our utility will only provide 15 minute usage in kWH and not a 15 minuted demand for residential services.

I think 15min kWH usage should be permitted to be used for demand (multiplied by 4 to get kW, that is), especially for resi. It's unclear to me that there is a robust standard that utilities follow for what constitutes the type of demand data referred to in the code. We've had discussions about the various formats of data before. So I'd appeal to the AHJ's sense of reason.

 

[don_resqcapt19]

I thought that was average power used over a 15 minute interval, so in units of kW it would just be 4 times 15 minute usage in kWh.

I though that was correct, but have been told over and over that it isn't.

 

[ron]

If the utility provides a demand value, it is typically over a 15 minute interval, so it is a 15 minute kWh value x 4, and you get kW demand as required by 220.87. Even better, my resi utility provides 5 minute kWh values, so then it is x12 to get and even more accurate demand than the NEC requires.

 

[ron]

I though that was correct, but have been told over and over that it isn't.

Lot of people want to use 1 month kWh values to figure out demand, but that is not good enough. Too much swings able to happen in a long average.

 

[jaggedben]

I though that was correct, but have been told over and over that it isn't.

What would be incorrect about it?

 

[don_resqcapt19]

What would be incorrect about it?

no idea, but when I posted to take the 15 minute usage and multiply by 4 to get a 15 minute demand on other sites, I was told that was not correct. When I do the math, I see it is correct, but a number of others told me no.

 

[retirede]

no idea, but when I posted to take the 15 minute usage and multiply by 4 to get a 15 minute demand on other sites, I was told that was not correct. When I do the math, I see it is correct, but a number of others told me no.

As long as you are using the largest 15 minute kWh in the entire period to be analyzed (month, year?), it should be close enough.

 

[don_resqcapt19]

As long as you are using the largest 15 minute kWh in the entire period to be analyzed (month, year?), it should be close enough.

you can download a year of data in a format that works with excel, so you can just sort the usage column from highest to lowest.

 

[jaggedben]

you can download a year of data in a format that works with excel, so you can just sort the usage column from highest to lowest.

I always do a MAX function. But that works too. Applying a color gradient can also be useful.